The present invention relates to a motion vector processing circuit for the processing of motion vector in correcting dynamic image in time-axis direction. This motion vector processing circuit is applicable, for example, to display devices such as the PDP (Plasma Display Panel) or LCD (Liquid Crystal Display) or the like having one frame divided into a plurality of subfields (or subframes) on time-sharing basis and being capable of displaying medium-gradation image.
Recently, the PDP and LCD have become popular as thin-type and large-screen display devices capable of displaying television pictures and the like. Conventionally, when displaying an image having medium-gradation such as that of a television picture, it has been a common practice to divide a frame into a plurality of subfields and make the subfields emit light according to the luminance level of input video signal. Such a display method of medium-gradation image differs from that of the CRT (Cathode Ray Tube) employing the dot-sequential scanning method. Therefore, some time lag occurs between the video signal generated by a television camera and a signal for display on a PDP or the like with respect to the display timing in a frame (or field), causing a blurring of the image of moving objects or formation of pseudo images. Therefore, according to prior art, in order to resolve such problems, the dynamic image is corrected by smoothing the amounts of movements of picture elements which form rapidly moving images on the basis of the detected motion vector within a frame of a video signal to be used for producing the image to be displayed.
However, as long as the motion vector processing for dynamic image correction is made on the basis of the motion vector detected within a frame, the processing in the time-axis direction adapted to the characteristic of human eye which works when following a moving object in a dynamic image cannot be applied, thereby giving rise to a problem that the corrected dynamic image will not match the function of human eye. For instance, when a motion vector detected on the basis of input video signal varies so rapidly during a frame that a human eye cannot follow, and a dynamic image is corrected on the basis of such a rapidly varying motion vector, this will cause the generation of dynamic image not harmonious with human eye.
The present invention is devised in consideration of the problems of the prior art and the object thereof lies in providing a motion vector processing circuit capable of performing the processing of motion vector in time-axis direction for enabling the dynamic image correction adapted to the movement of human eye.
The present invention relates to a motion vector processing circuit for correcting the dynamic image display characteristics of a display device having a frame divided into a plurality of subfields, the motion vector processing circuit comprising a motion vector difference detection means for detecting the differences among the motion vectors of N (N= any integer not smaller than 2) number of frames of video signals of the image to be displayed, a variation determination means for determining whether the value of the difference detected by the motion vector difference detection means is smaller than a preset value L1 or not, and an output control means for outputting the motion vector of a corresponding frame when the value of the detected difference is determined to be smaller than the preset value L1 by the variation determination means and outputting the motion vector of a frame, preceding the corresponding frame, having a detected difference smaller than the present value L1, when the detected difference is determined to exceed the preset value L1.
When the variation of the motion vector between given frames is small, that is, when the value of difference detected by the motion vector detection means is smaller than the preset value L1, the value of detected difference is determined to be less than the preset value L1 by the variation determination means, so that the motion vector of the corresponding frame is output from the output control means. When the variation of the motion vector between given frames is relatively large, that is, when the value of difference detected by the motion vector difference detection means exceeds the preset value L1, the value of the detected difference is determined to exceed the preset value L1 by the variation determination means, so that the motion vector of a frame, preceding the corresponding frame, having a detected difference smaller than the preset value L1 is output. Therefore, when the variation of the motion vector is relatively small, it becomes possible for the dynamic image to be corrected by the motion vector of the corresponding frame. On the other hand, when the variation of the motion vector is relatively large, it is possible for the dynamic image to be corrected by a motion vector whose variation is smaller than that of the motion vector of the corresponding frame, whereby a dynamic image display harmonious with the function of the human eye can be realized.
Further, in the motion vector processing circuit according to the present invention, the motion vector difference detection means detects the difference D1 between the motion vector of a present frame and the motion vector of the immediately following frame and the difference D2 between the motion vector of the present frame and that of the immediately preceding frame; the variation determination means determines whether both the differences D1 and D2 is less than the preset value L1; the output control means outputs the motion vector of the present frame when both the differences D1 and D2 are determined to not exceed the preset value L1, and outputs the motion vector of a frame, preceding the present frame, whose difference exceeds the preset value L1, when at least one of the differences D1 and D2 is determined to exceed the preset value L1. When the circuit is composed in this way, construction of each component can be simplified.
Further, the variation determination means is additionally provided with a function to determine whether or not both the differences D1 and D2 exceed the preset value L1, and the output control means is additionally provided with a function to output the motion vector having value of 0 (i.e., the value of motion vector =0) when both the differences D1 and D2 are determined to be exceeding the preset value. L1. Thus, where the circuit is composed in this way, when both the differences D1 and D2 exceed the preset value L1, the output control means will not output the zero-value motion vector for correcting dynamic image, whereby excessive correction of dynamic image can be prevented even in such a case where the motion vector varies largely during successive 2 or more frames.
Further, the variation determination means is additionally provided with a function for determining whether or not the absolute values of both the differences D1 and D2 are exceeding the preset value L1, and the output control means is additionally provided with a function for outputting zero-value motion vector when it is determined that the absolute values of both the differences D1 and D2 exceed the preset value L1 and the absolute value of the sum of the differences D1 and D2 and a function for inhibiting output of zero-value motion vector when the absolute value of the sum of the differences D1 and D2 is less than the preset value L1 even if the absolute values of both the differences D1 and D2 exceed the preset value L1. When the circuit is composed in this way, even when the absolute values of both the differences D1 and D2 are exceeding the preset value L1, the output control means outputs zero-value motion vector only when the absolute value of the sum of the differences D1 and D2 is exceeding the preset value L1 and inhibit the output of the zero-value motion vector when the absolute value of the sum of the differences D1 and D2 is less than the preset value L1, whereby the dynamic image can be corrected in consideration of the direction of variation of the motion vector.
Further, the motion vector difference detection means is composed of a first frame memory and a second frame memory for outputting an input motion vectors after sequentially giving a time lag corresponding to each frame, a first difference-computation arithmetic unit for calculating the difference D1 between the motion vector input to the first frame memory and the motion vector output from the first frame memory, a second difference-computation arithmetic unit for computing the difference D2 between the motion vector output from the first frame memory and the motion vector output from the second frame memory. When the above means is composed in this way, the motion vector difference detection stage can be composed of two frame memories and 2 difference-computation arithmetic units.
Further, the motion vector difference detection means comprises the first frame memory for outputting an input motion vector after giving a time lag corresponding to one frame, the difference-calculation arithmetic unit for calculating the difference D1 between the motion vector input to this first frame memory and the motion vector output from the first frame memory, and the second memory frame for outputting the difference D1 calculated by the difference-calculation arithmetic unit after giving a time lag corresponding to one frame. When composed in this way, the motion vector difference detection means can be composed of two frame memories and 1 difference-calculation arithmetic unit.